Current mode bang-bang regulator amplifier

ABSTRACT

An improved CMBB regulator includes a current amplifier circuit that allows both load transient performance and noise immunity to be optimized simultaneously. The current amplifier circuit measures a voltage drop across a sense resistor to determine a power driver output current. The current amplifier circuit separates AC and DC current information and applies separate gain factors to the AC and DC current information. AC and DC current information modified by the gain factors is then recombined and used to pass current through an output resistor. A current amplifier output voltage is input to a comparator circuit that provides an output that indicates whether the current amplifier output voltage is above, equal to, or below a desired voltage level. The comparator output is then used to provide feedback control to a power driver circuit.

SUMMARY

Implementations described herein provide a current amplifier circuitthat removes an in-line resistor from a typical CMBB regulator andallows both load transient performance and noise immunity to beoptimized simultaneously. An example CMBB regulator according to thepresently disclosed technology includes a current amplifier circuitwithin a controller and a power driver circuit. The controller couples acontroller output to a feedback input of the power driver circuit.

The current amplifier circuit includes a sense resistor, an outputresistor, and a gain and filter circuit. The gain and filter circuitmeasures a voltage drop across the sense resistor to determine the powerdriver output current. Since the resistance value of the sense resistoris related to the resistance value from the power driver output andthrough the load, the current in amplifier output is related to thecurrent of the power driver output and can be positive or negative. Thegain and filter circuit then separates AC and DC current information andapplies separate gain factors to the AC and DC current information. ACand DC current information modified by the gain factors is thenrecombined and used to pass current through the output resistor.

A current amplifier output voltage, which is a combination of Vout andthe current flowing across the sense resistor, is input to a comparatorcircuit that provides a comparator output that indicates whether thecurrent amplifier output voltage is above, equal to, or below a desiredvoltage level. The comparator output is then used to provide feedbackcontrol to the power driver circuit. The current amplifier outputvoltage and Vout are fed into a soft start/current limiter that limits avoltage difference between the current amplifier output voltage and Voutduring a start-up time to provide a soft start.

Other implementations are also described and recited herein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 illustrates an example computer equipped with a motherboard and ahard disk drive with an improved CMBB regulator.

FIG. 2 illustrates an idealized power driver output waveform in animproved CMBB regulator.

FIG. 3 illustrates an example improved CMBB regulator that includes acurrent amplifier circuit within a controller and a power drivercircuit.

FIG. 4 illustrates an example current amplifier circuit connected to apower driver circuit and a load.

FIG. 5 illustrates an example gain and filter circuit that separates andindependently amplifies AC and DC components of an amplifier current.

FIG. 6 illustrates example operations for separately amplifying AC andDC components of a power driver output current and using the amplifiedcurrent for an improved CMBB regulator control.

FIG. 7 illustrates a plan view of an example disc drive.

DETAILED DESCRIPTIONS

A typical current mode bang-bang (CMBB) regulator uses an in-line senseresistor (e.g., a discrete resistor or a copper trace resistor) to sensepower driver current. However, the in-line resistor can be undesirablebecause the resistor takes space on a CMBB circuit board, consumes poweroutput from a power driver circuit to a load, and adds an expense to thecircuit. Still further, typical CMBB regulators cannot be optimized tosimultaneously improve both load transient performance and noiseimmunity (i.e. signal-to-noise ratio (SNR)). Generally, lower in-linesense resistor values improve load transient performance but worsennoise immunity. Similarly, higher in-line sense resistor values improvenoise immunity but worsen load transient performance.

FIG. 1 illustrates an example computer 160 equipped with a motherboard162 and a hard disk drive (HDD) 164 with an improved CMBB regulator 100.The computer 160 is any server, desktop, laptop, or other computingsystem. The computer, 160, for example, operatively couples varioussystem components (e.g., HDD 164) using at least the motherboard 162. Inone implementation, the motherboard 162 and the HDD 164 are connectedtogether via a Serial ATA interface 166, however, other connectionschemes are contemplated. Through the motherboard 162, the computercontrols operation of the HDD 164.

Both the motherboard 162 and the HDD 164 are powered by a power supply168 that may convert incoming AC power to DC power, step down anincoming voltage, step-up the incoming voltage, and/or limit currentavailable to the motherboard 162 and the HDD 164. In one implementation,power for the HDD 164 comes from the power supply 168 through themotherboard 162.

The HDD 164 is equipped with a disk pack 170, which is mounted on aspindle motor (not shown). The disk pack 170 includes one or moreindividual disks, which rotate in a direction indicated by arrow 172about a central axis 174. Each disk has an associated disc read/writehead slider 176 for communication with the disk surface. The slider 176is attached to one end of an actuator arm 178 that rotates about a pivotpoint 179 to position the slider 176 over a desired data track on a diskwithin the disk pack 170.

The HDD 164 is also equipped with a printed circuit board (PCB) 180 thatcontrols operation of the HDD 164. The PCB 180 may include asystem-on-a-chip (SOC) 182 that combines some, many, or all functions ofthe PCB 180 on a single integrated circuit. Alternatively, the functionsof the PCB 180 may be spread out over a number of integrated circuitswithin one package (i.e., SIP). In the implementation of FIG. 1, theimproved CMBB regulator 100, discussed further with regard to FIGS. 2-6,regulates voltages within the SOC 182 used to write and/or read datafrom the disk pack 170. The HDD 164 is discussed further with regard toFIG. 7.

FIG. 2 illustrates an idealized power driver output waveform 200 in animproved CMBB regulator. A vertical axis 284 represents power driveroutput voltage and a horizontal axis 286 represents time. A power drivercircuit includes switches that alternatively connect the driver outputto voltage VDD at 288 or voltage VSS at 290, with transitional orswitching intervals separating the conduction times of the switches toensure that both switches are not conducting at the same time.

The power driver output alternates between ON pulses 292 and OFF pulses294 as illustrated. Each ON pulse 292 has an on time TON. Each off timeinterval 294 has an off time TOFF. A complete cycle of the power driveroutput can run from a start time of an ON pulse to a start time of thenext-in-time ON pulse. The complete cycle has a time duration ofTON+TOFF. A duty cycle of the power driver output is defined as DUTYCYCLE=TON/(TON+TOFF). A frequency of the power driver output is definedas 1/(TON+TOFF). The improved CMBB regulator, discussed with morespecificity below, adapts actual power driver output to match theidealized power driver waveform as closely as possible in real time.

FIG. 3 illustrates an example improved CMBB regulator 300 that includesa current amplifier circuit 302 within a controller 304 and a powerdriver circuit 306. The controller 304 couples a controller output 322to a feedback input 308 of the power driver circuit 306. The powerdriver circuit 306 includes synchronous driver logic 316, a high-side(HS) gate driver 308, a low-side (LS) gate driver 310, a high-side (HS)power transistor 312, and a low-side (LS) power transistor 314 (e.g.,MOSFETS). The power driver circuit 306 alternatively connects a powerdriver output 324 to a positive voltage drain (VDD) or common DC voltagesource (VSS), with transitional or switching intervals separating theconduction times of the transistors 312, 314 to ensure that both thetransistors 312, 314 are not conducting at the same time.

More specifically, activating the HS transistor 312 connects thepositive VDD rail to the power driver output 324 and activating the LStransistor 314 connects the DC common VSS to the power driver output324. The synchronous driver logic 316 ensures that only one of thetransistors 312, 314 is activated at any particular instant, therebyavoiding a short circuit between the VDD and the VSS rails. Alternationbetween the HS transistor 312 and the LS transistor 314 results in aperiodic power driver output signal between ON pulses (VDD magnitude)and OFF pulses (VSS magnitude).

There is also a sense HS transistor 326 and a sense LS transistor 328within the current amplifier 302 that are each operated in parallel withthe transistors 312, 314 but have an amplifier output that is connectedto the sense resistor 354 before proceeding to the load 418. The senseHS transistor 326 may act as a current mirror to the HS transistor 312and similarly, the sense LS transistor 328 may act as a current mirrorto the LS transistor 314. The current mirrors copy current through oneactive device (e.g., HS transistor 312) by controlling current inanother active device (e.g., sense HS transistor 326) of a circuit,keeping the load current constant regardless of loading. In oneimplementation, the sense HS transistor 326 and the sense LS transistor328 create a current proportional to the current through HS transistor312 and LS transistor 314, respectively, but with less magnitude to passthrough the sense resistor 354. As a result, sense resistor 354 has noeffect on Vout 334 in the improved CMBB regulator 300. Various types ofsolid state switches (e.g., MOSFETS, BJTs, FETS) may be used as thetransistors 312, 314, 326, and 328 and free wheeling diodes may beplaced across the transistor outputs, as needed or desired.

The HS or LS output of drivers 308, 310 couples the power driver output324 to a load 318, and maintains a relatively constant load voltage Vout334 at the load 318. Further, a low pass filter 352 may be coupled tothe power driver output 324 to reduce high frequency noise that reachesthe load 318. The low pass filter 352, for example, may include aninductor 348 and one or more capacitors 350.

The current amplifier circuit 302 obtains and separates AC and DCcurrent information flowing across a sense resistor 354, with these ACand DC components being equal or related to the power driver output 324current. The current amplifier circuit 302 then converts the AC and DCcurrent information into separate AC and DC voltages. A gain and filtercircuit 336 may separately filter and/or amplify the AC voltage and DCvoltage. The filtered and/or amplified AC voltage and DC voltage arethen recombined and are used to pass current through an output resistor356. The operation of the current amplifier circuit 302 will bediscussed in more detail with regard to FIGS. 3 and 4.

The controller output 322 has a duty cycle that varies as a function ofthe current amplifier output voltage 332 from the current amplifiercircuit 302. The controller 304 provides closed loop control of thepower driver circuit 306. The duty cycle at controller output 322 isconstant when the power driver output 324 current is fixed and variablewhen the power driver output 324 current is variable.

The current amplifier output voltage 332 is based on a combination ofVout 334 and the current flowing through output resistor 356. Thecurrent flowing through output resistor 356 is related to the voltagedrop across sense resistor 354 according to the gain and filter circuit336. The controller 304 also includes a comparator circuit 320 thatreceives the current amplifier output voltage 332 and provides acomparator output 338 that indicates whether the current amplifieroutput voltage 332 is above, equal to, or below a reference voltagelevel. The controller 304 further includes a soft start/current limiter340 that limits a voltage difference between the current amplifieroutput voltage 332 and Vout 334 during a start-up time to provide a softstart. The soft start/current limiter 340 prevents large inrush currentsfrom occurring during the start-up time.

The controller 304 also includes a pulse generator 342 that receives thecomparator output 338. The comparator output 338 controls or triggersthe pulse generator 342 to generate and output a pulsing signal 344. Thepulsing signal 344 has a fixed pulse width when the comparator output338 indicates that the current amplifier output voltage 332 is equal tothe desired level. Spacing between the fixed pulses in the pulsingsignal 344 (i.e., the duty cycle) are adjusted for changes in the load318. In some implementations, the fixed pulse width corresponds to ONpulses (VDD magnitude). In other implementations, the fixed pulse widthcorresponds to OFF pulses (VSS magnitude).

The controller 304 further includes a time limit circuit 346 thatreceives the pulsing signal 344 from the pulse generator 342. The timelimit circuit 346 passes on or replicates a portion of the pulses withinthe pulsing signal 344 as the controller output 322. The time limitcircuit 346 may pass on some, most, or all of the fixed pulses withinthe pulsing signal 344 based on the spacing between the fixed pulses.While the time limit circuit 346 generally passes most of the pulses onto the controller output 322, when the fixed pulses are too closelyspaced, the time limit circuit 346 blanks, or does not pass, some of theclosely spaced fixed pulses to the controller output 322. In effect, thetime limit circuit 346 limits a time between fixed pulses of the pulsingsignal 344 from the pulse generator 342 to a minimum value. Morespecifically, when the pulsing signal 344 includes ON pulses, the timelimit circuit 346 limits an OFF time to a minimum value. Similarly, whenthe pulsing signal 344 includes OFF pulses, the time limit circuit 346limits an ON time to a minimum value. The minimum time value (either ONor OFF) limits a frequency of a noise at the power driver output 324 toa maximum frequency.

In various implementations, one or more of the controller 304, powerdriver circuit 306, and low pass filter 352 are foamed as an integratedcircuit or a multi-chip module. Other functional blocks can also beincluded in the integrated circuit. Further, the components of theintegrated circuit may be produced on one silicon chip for low-costproduction. Still further, the integrated circuit may be predominantly adigital integrated circuit, thus limiting the use of complex linearamplifier circuitry that is space intensive on a silicon chip. In oneexample implementation, the controller 304 and the power driver circuit306 are formed in the integrated circuit. As a result, the onlycomponents of the improved CMBB regulator 300 outside of the integratedcircuit are the low pass filter 352 and the load 318.

FIG. 4 illustrates an example current amplifier circuit 402 connected toa power driver circuit 406 and a load 418. The current amplifier circuit402 includes sense transistors 426, 428, a sense resistor 454, an outputresistor 456, and a gain and filter circuit 436. Similar to the powerdriver circuit 306 of FIG. 3, the current amplifier circuit 402 of FIG.4 is equipped with an HS transistor 426 and a LS transistor 428. Thesense transistors 426, 428 are operated in parallel with the transistors310, 312 but have an amplifier output 430 that is connected to the senseresistor 454 before proceeding to the load 418. More specifically,activating the sense HS transistor 426 connects a positive VDD rail tothe amplifier output 430 and activating the LS transistor 428 connects aDC common VSS to the amplifier output 430. In the implementation shown,only the HS sense transistor 426 or the LS sense transistor 428 isoperated at any given time to prevent a short circuit condition betweenVDD and VSS. In one implementation, the sense HS transistor 426 and thesense LS transistor 428 create a current proportional to the currentthrough HS transistor 312 and LS transistor 314 of FIG. 3, respectively,but with less magnitude to pass through the sense resistor 454.

The gain and filter circuit 436 measures a voltage drop across the senseresistor 454 to determine the current in amplifier output 430. The gainand filter circuit 436 then separates AC and DC current information inthe amplifier output 430 and converts the AC and DC current informationinto a separate AC voltage and a DC voltage that passes current throughthe output resistor 456. The gain and filter circuit 436 may alsoseparately filter and/or amplify the AC voltage and DC voltage. Freedomto choose different gains for the AC and DC components of the amplifieroutput 430 allows both load transient performance and noise immunity tobe improved since DC current step controls load current transientperformance and AC current amplitude controls noise immunity. In oneimplementation, gain for the AC component is greater than the gain forthe DC component to optimize transient performance and noise immunity.The operation of the gain and filter circuit 436 will be discussed inmore detail with regard to FIG. 5.

In one implementation, the resistance value of the active sensetransistor (i.e. HS sense transistor 426 or LS sense transistor 428) ismuch larger than the resistance of the sense resistor 454. Voltageacross the output resistor 456 forms a floating voltage that is added tothe output voltage (Vout). This floating voltage acts as a ripplecomponent to the output voltage that is used to control switchingfrequency in an improved CMBB regulator. Thus, Vout and voltage acrossthe sense resistor 454 are fed back into the control loop. Morespecifically, the following equation defines the current across thesense resistor 454.

I _(sense) =K _(sense)*{K_(dc) K _(dc) *F _(LPF) [I _(inductor) ]+K_(ac) *F _(HPF) [I _(inductor)]}

where,

I_(sense) is the current through the sense resistor 454;

K_(sense) is a current gain ratio of sense transistor 426, 428 and amain transistor 312, 314, which is a function of the resistance of thesense resistor 454;

K_(dc) is a DC component gain applied by the gain and filter circuit436;

F_(LPF) is a low pass filter function;

I_(inductor) is current through an output inductor;

K_(ac) is an AC component gain applied by the gain and filter circuit436; and

F_(HPF) is a high pass filter function.

FIG. 5 illustrates an example gain and filter circuit 536 that separatesand independently amplifies AC and DC components of a sense current. Thegain and filter circuit 536 measures a voltage drop across a senseresistor 554 to determine the current (I_(sense)) flowing to a load. Thevoltage drop is fed into a transconductance filter/amplifier (e.g.,G_(m) filter 502) that applies a gain that converts the voltage acrosssense resistor 554 to current through sense resistor 554. Positive andnegative outputs of the G_(m) filter 502 are fed into anothertransconductance filter/amplifier that is also equipped with a capacitor(e.g., G_(m)-C filter 504) that may incorporate a low-pass filter andmay use a capacitor 510 to remove the AC component of the calculatedcurrent through sense resistor 554 and output positive and negativevoltages corresponding only to the DC component of the calculatedcurrent through sense resistor 554.

In a first branch 522 of the gain and filter circuit 536, a DC gainfactor (K_(dc)) 506 is applied to the positive output of the G_(m)-Cfilter 504. In a second branch 520 of the gain and filter circuit 536,the positive output of the G_(m)-C filter 504 is subtracted from thepositive output of G_(m) filter 502 in subtraction block 512 resultingin only the positive AC component of the calculated current through thesense resistor 554. An AC gain factor (K_(ac)) 508 is applied to the ACcomponent of the positive calculated current through sense resistor 554.

In a third branch 524 of the gain and filter circuit 536, a DC gainfactor (K_(dc)) 506 is applied to the negative output of the G_(m)-Cfilter 504. In a fourth branch 526 of the gain and filter circuit 536,the negative output of the G_(m)-C filter 504 is subtracted from thenegative output of G_(m) filter 502 in subtraction block 514 resultingin only the negative AC component of the calculated current through thesense resistor 554. An AC gain factor (K_(ac)) 508 is applied to the ACcomponent of the negative calculated current through sense resistor 554.

Addition block 516 combines the DC positive output of the G_(m)-C filter504 with the AC positive output of the G_(m)-C filter 504 afterapplication of K_(dc) 506 and K_(ac) 508. Addition block 518 combinesthe DC negative output of the G_(m)-C filter 504 with the AC negativeoutput of the G_(m)-C filter 504 after application of K_(dc) 506 andK_(ac) 508. The resulting combined positive and negative outputs of theG_(m)-C filter 504 are used to pass current through an output resistor556 and the resulting voltage across the output resistor 556 is used forfeedback control of an improved CMBB regulator.

More specifically, current amplifier output voltage 532, which is acombination of Vout 334 and the current flowing across sense resistor554, is input to a comparator circuit that provides a comparator outputthat indicates whether the current amplifier output voltage 532 isabove, equal to, or below a desired voltage level. The comparator outputis then used to provide feedback control to a power driver circuit. Thecurrent amplifier output voltage 532 and Vout 534 may also be fed into asoft start/current limiter that limits a voltage difference between thecurrent amplifier output voltage 532 and Vout 534 during a start-up timeto provide a soft start.

An RC filter may be used in place of the G_(m)-C filter 504, however,the G_(m)-C filter 504 may be preferred due to a smaller capacitancerequirement. In the implementation shown, only one filter is used toselectively implement both a low-pass and high-pass filter. Use of onefilter circuit minimizes the amount of die size occupied by the G_(m)-Cfilter 504. In other implementations, two parallel G_(m)-C filters maybe used, one high-pass and one low-pass. A low-pass transfer function ofthe G_(m)-C filter 504 is shown below.

${\frac{I_{out}}{I_{in}} = \frac{1}{1 + \frac{sc}{{Gm}\; 1}}};$

where,

I_(out) is current flowing out of the G_(m)-C filter 504;

I_(in) is current flowing into the G_(m)-C filter 504;

c is capacitance of the G_(m)-C filter 504; and

Gm1 is transconductance gain of the G_(m)-C filter 504.

A high-pass transfer function of the G_(m)-C filter 504 may be achievedby using a signal minus output of the low-pass filter. An examplehigh-pass transfer function of the G_(m)-C filter 504 is shown below.The high-pass and low-pass transfer functions are frequency domainrepresentations of filter response of the G_(m)-C filter 504.

$\frac{I_{out}}{I_{in}} = {{1 - \frac{1}{1 + \frac{sc}{{Gm}\; 1}}} = {\frac{\frac{sc}{{Gm}\; 1}}{1 + \frac{sc}{{Gm}\; 1}}.}}$

An example calculation of the current across the output resistor 556 asa function of the current across the sense resistor 554 is as follows.

$\begin{matrix}{I_{output} = {{\left( {K_{dc} + K_{ac}} \right)*I_{sense}} - {K_{ac}*{F_{LPF}\left\lbrack I_{sense} \right\rbrack}}}} \\{= {{K_{dc}*I_{sense}} + {K_{ac}*\left\{ {1 - {F_{LFP}\left\lbrack I_{sense} \right\rbrack}} \right\}}}} \\{{= {{K_{dc}*I_{sense}} + {K_{ac}*{F_{HPF}\left\lbrack I_{sense} \right\rbrack}}}};}\end{matrix}$

where,

I_(output) is current through the output resistor 556;

K_(dc) is a DC component gain applied by the gain and filter circuit536;

K_(ac) is an AC component gain applied by the gain and filter circuit536;

I_(sense) is current through the sense resistor 554;

F_(LPF) is a low pass filter function; and

F_(HPF) is a high pass filter function.

FIG. 6 illustrates example operations 600 for separately amplifying ACand DC components of a power driver output current and using theamplified current for improved CMBB regulator control. In a receivingoperation 605, current is received through a sense resistor. The currentflowing through a sense resistor is related (e.g., equal orproportional) to a current flowing through an output inductor to a load.In a measuring operation 610, current flowing through the sense resistoris measured by detecting the voltage drop across the sense resistor.

In an applying operation 615, one or more filters may be applied to thevoltage measurement. The filters may be high-pass, low-pass, orband-pass and may operate to remove undesirable noise from the voltagemeasurement. In some implementations, no filters are applied to thevoltage measurement. In a separating operation 620, AC and DC componentsof the voltage measurement are separated into two separate signals. Inan applying operation 625, an AC gain factor is applied to the AC signaland a DC gain factor is applied to the DC signal. The gain factor mayoperate to amplify the AC and/or DC signals, compress the AC and/or DCsignals, or pass the AC and/or DC signals on unchanged.

In a recombining operation 630, the AC and DC components of the voltagemeasurement, after application of the gain factors, are recombined andare applied to an output resistor. In a first supplying operation 635,both the recombined voltage and an output voltage corresponding tovoltage at a load are supplied to a comparator circuit for the improvedCMBB regulator. In a second supplying operation 635, the recombinedvoltage and the output voltage are supplied to a current limitingcircuit that limits start-up current for the improved CMBB regulator.

FIG. 7 illustrates a plan view of an example disc drive 700. The discdrive 700 includes a base 702 to which various components of the discdrive 700 are mounted. A top cover 704, shown partially cut away,cooperates with the base 702 to form an internal, clean environment forthe disc drive in a conventional manner. The components include aspindle motor 706 that rotates one or more storage medium discs 708 at aconstant high speed. Information is written to and read from tracks onthe discs 708 through the use of an actuator assembly 710, which rotatesduring a seek operation about a bearing shaft assembly 712 positionedadjacent the discs 708. The actuator assembly 710 includes a pluralityof actuator arms 714 that extend towards the discs 708, with one or moreflexures 716 extending from each of the actuator arms 714. Mounted atthe distal end of each of the flexures 716 is a head 718 that includesan air bearing slider enabling the head 718 to fly in close proximityabove the corresponding surface of the associated disc 708. The distancebetween the head 718 and the storage media surface during flight isreferred to as the fly height.

During a seek operation, the track position of the head 718 iscontrolled through the use of a voice coil motor (VCM) 724, whichtypically includes a coil 726 attached to the actuator assembly 710, aswell as one or more permanent magnets 728 which establish a magneticfield in which the coil 726 is immersed. The controlled application ofcurrent to the coil 726 causes magnetic interaction between thepermanent magnets 728 and the coil 726 so that the coil 726 moves inaccordance with the well-known Lorentz relationship. As the coil 726moves, the actuator assembly 710 pivots about the bearing shaft assembly712 and the transducer heads 718 are caused to move across the surfacesof the discs 708.

The spindle motor 706 is typically de-energized when the disc drive 700is not in use for extended periods of time. The transducer heads 718 aremoved away from portions of the disk 708 containing data when the drivemotor is de-energized. The transducer heads 718 are secured overportions of the disk not containing data through the use of an actuatorlatch arrangement and/or ramp assembly 744, which prevents inadvertentrotation of the actuator assembly 710 when the drive discs 708 are notspinning.

A flex assembly 730 provides the requisite electrical connection pathsfor the actuator assembly 710 while allowing pivotal movement of theactuator assembly 710 during operation. The flex assembly 730 includes aprinted circuit board 734 to which a flex cable connected with theactuator assembly 710 and leading to the head 718 is connected. The flexcable may be routed along the actuator arms 714 and the flexures 716 tothe transducer heads 718. The printed circuit board 734 typicallyincludes circuitry for controlling the write currents applied to thetransducer heads 718 during a write operation, a preamplifier foramplifying read signals generated by the transducer heads 718 during aread operation, and a power supply to a head heater, which allows finehead to disk clearance control by setting the head temperature near theactive head elements. The flex assembly 730 terminates at a flex bracketfor communication through the base deck 702 to a disc drive printedcircuit board (not shown) mounted to the bottom side of the disc drive700.

The printed circuit board 734 can include the improved CMBB regulator ofFIG. 1 and FIG. 3 and a system-on-a-chip (SOC). The improved CMBBregulator regulates voltages within the SOC and is used to write and/orread data from the disk 708. In other implementations, there is no SOCand the improved CMBB regulator regulated voltages in other componentson the printed circuit board 734.

The embodiments of the invention described herein are implemented aslogical steps in one or more computer systems. The logical operations ofthe present invention are implemented (1) as a sequence ofprocessor-implemented steps executing in one or more computer systemsand (2) as interconnected machine or circuit modules within one or morecomputer systems. The implementation is a matter of choice, dependent onthe performance requirements of the computer system implementing theinvention. Accordingly, the logical operations making up the embodimentsof the invention described herein are referred to variously asoperations, steps, objects, or modules. Furthermore, it should beunderstood that logical operations may be performed in any order, unlessexplicitly claimed otherwise or a specific order is inherentlynecessitated by the claim language.

The above specification, examples, and data provide a completedescription of the structure and use of exemplary embodiments of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended. Furthermore, structuralfeatures of the different embodiments may be combined in yet anotherembodiment without departing from the recited claims.

1. A method of passing current through an output resistor for regulatingdriver voltage comprising: combining a modified AC component obtained byapplying an AC gain factor to an AC component of a current flowingthrough an input resistor with a modified DC component obtained byapplying a DC gain factor to a DC component of the current flowingthrough the input resistor to pass current through the output resistor.2. The method of claim 1, further comprising: measuring a voltage dropacross the input resistor to find the AC component of the currentflowing through the input resistor and the DC component of the currentflowing through the input resistor.
 3. The method of claim 2, wherein alow-pass filter is applied to the measured voltage to reduce noise. 4.The method of claim 1, wherein the current flowing through the inputresistor is related to current flowing to a load.
 5. The method of claim1, wherein the modified AC component is used to regulate driver voltageswitching frequency.
 6. The method of claim 1, wherein the modified DCcomponent is used to limit start-up current in a power driver.
 7. Themethod of claim 1, wherein a voltage drop across the input resistor doesnot directly affect power driver output voltage.
 8. A circuit forregulating voltage in a power driver, the circuit comprising: a currentamplifier adapted to measure current flowing through an input resistor,separate AC and DC components of the current flowing through an inputresistor, and apply an AC gain factor to the AC component and a DC gainfactor to the DC component.
 9. The circuit of claim 8, wherein thecurrent flowing through the input resistor is measured using adifferential voltage across the input resistor and the AC and DCcomponents of the current are represented by voltages.
 10. The circuitof claim 8, wherein the current amplifier is further adapted torecombine the AC and DC components of the current and pass therecombined current through an output resistor using the recombinedcurrent.
 11. The circuit of claim 9, further comprising: a comparatoradapted to compare an AC component of the measured voltage with areference voltage and output an indication of whether the measuredvoltage is above or below the reference voltage.
 12. The circuit ofclaim 9, further comprising: a current limiter adapted to limit a DCcomponent of the measured voltage during start-up time to provide a softstart.
 13. The circuit of claim 11, further comprising: a pulsegenerator adapted to generate and output a pulsing signal with a fixedpulse width corresponding to the reference voltage.
 14. The circuit ofclaim 13, further comprising: a time limiter adapted to limit a timebetween the fixed pulses of the pulsing signal to a minimum value. 15.The circuit of claim 13, wherein the power driver is adapted to receivethe pulsing signal from the pulse generator and alternatively connect apower driver output to a positive VDD or common DC VSS in sequence withthe pulsing signal.
 16. The circuit of claim 15, further comprising: alow-pass filter adapted to remove high-frequency noise from the powerdriver output.
 17. The circuit of claim 8, wherein a voltage drop acrossthe input resistor does not directly affect power driver output voltage.18. A method of regulating power driver output voltage to a load using acurrent amplifier, the method comprising: proportionally replicating aload current as a sense current applied to an input resistor; detectinga voltage drop across the input resistor; calculating the load currentbased on the voltage drop across the input resistor; varying voltageoutput from the current amplifier based on the load.
 19. The method ofclaim 18, wherein the input resistor is coupled in parallel with a loadcurrent path.
 20. The method of claim 18, wherein the varied voltageoutput from the current amplifier is used to generate a feedback currentthat controls a power driver output waveform.